Solenoid valves are used in various industrial fields. Patent Literature 1 discloses a solenoid valve used to supply a fuel to an engine.
The solenoid valve of Patent Literature 1 includes a valve plug and an armature extending from the valve plug toward a coil. The valve plug and the armature are coupled to each other with a screw.
Since the armature of Patent Literature 1 is formed of a member separate from the valve plug, a solenoid valve formed in accordance with the technique disclosed in Patent Literature 1 tends to have a large structure. The Inventors of the present invention devised a small solenoid valve different from the solenoid valve of Patent Literature 1. This small solenoid valve includes a movable piece constituted by an armature and a valve plug integrated together. The Inventors operated the small solenoid valve for a long period and tested the performance thereof. As a result of the performance test, it was found that the response performance of the solenoid valve produced by the Inventors drops significantly after a certain period of time from start of the test.